In producing rabbit antisera to S. mutans serotype c whole cells, investigators have suggested a variety of procedures and immunization schedules. Prior experiments suggest that the I.V. route was the only method that produced high titers, but a high mortality rate was associated with the booster injections. To overcome these deficiencies, several experiments were conducted to study variations of a multiple site immunization schedule suggested by investigators at Hazelton Laboratories. In additional, it has been reported that rabbits immunized with different serotype c strains exhibit different levels of anaphylactic response. The strains least associated with fatal anaphylactic responses were studied as antigens to produce antisera and reduce loss during booster injections. Vaccine concentrations during booster series were also varied to assess the dose effect on toxicity and the production of high titered antisera.